TCAS RA response should not be used as a primary separation tool in controlled airspace because it introduces another hazard for all other airspace users. Upon complying with RA commands that aircraft then becomes an unknown factor to air traffic control and is, therefore, uncontrolled. All other (controlled!) aircraft must be protected from an aircraft carrying out manoeuvres that are unknown to ATC. This is a little like placing an aircraft in a situation where a go-round is possible however ATC are aware of this potential and can provide a contingency plan. With TCAS RA there is no prior awareness that the manoeuvre may take place - strategic ATC moves to tactical ATC with lots of unknowns - not good. I support aircrew following RA commands except under exceptional circumstances - captain must always have veto.
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